FACTORS RESPONSIBLE FOR THE DIFFERENTIAL PROCOAGULANT EFFECTS OF DIVERSE PLASMINOGEN ACTIVATORS IN PLASMA

This study was designed to define the procoagulant effects of different plasminogen activators in recalcified plasma. Accordingly, a two-stage assay procedure was developed in which citrated plasma was recalcified and incubated for 1-7 min with streptokinase (SK), urokinase (UK), or tissue-plasminogen activator (t-PA). An aliquot of this first-stage plasma was added to second-stage plasma; procoagulant activity was measured as the acceleration of the clotting time compared with that in control first-stage plasma to which plasminogen activators had not been added. With this procedure, second-stage clotting times were significantly accelerated after activation of plasminogen compared with those in control plasma and were shortest with 1000 i.u./ml SK. The presence of increased thrombin activity in the recalcified citrated plasma was verified by measurement of increased concentrations of fibrinopeptide A, which were inhibited by addition of 1 U/ml hirudin or 0.5 U/ml heparin to plasma during incubation with the plasminogen activators. Activation of factor X was induced in plasma incubated with SK. The rate of activation of factor X was increased when thrombin was elaborated. Induction of procoagulant activity was found to be dependent on depletion of alpha-2-antiplasmin and on the presence of plasmin activity in plasma, and could be inhibited by aprotinin. Thus, procoagulant activity in response to pharmacologic activation of plasminogen is dependent on plasmin-mediated activation of factor X, and subsequent activation of prothrombin.